Boss Mustang

  • 06-Apr-2011 06:58 EDT

Chief engineer Dave Pericak promised he would deliver a true Boss 302 that could beat the BMW M3 on the racetrack and not a "wheel and sticker package."

In 1968 Ford sought to create the finest-handling American car and developed the 1969 Mustang Boss 302 specifically to attack the Sports Car Club of America’s Trans-Am racing series. Four decades later, the Boss name unsullied by use on unworthy pretenders like the Mustang II Cobra II of the mid-‘70s, Ford sought to reclaim the magic. This time the company set the benchmark of outracing the esteemed BMW M3 around Laguna Seca raceway as its goal.

If engineers could finesse the solid-rear-axle Mustang into a form that could beat the Bimmer, Ford execs would approve the project, explained Jim Farley, Group Vice President of Global Marketing, Sales and Service. “They were not going to do this project if they could not beat the M3 at the track,” he said.

Taking up that challenge demanded a thorough rework of the car. “The Boss 302 isn’t something a Mustang GT owner can buy all the parts for out of a catalog or that a tuner can get by adding a chip,” noted Chief Engineer David Pericak. “This is a front-to-back re-engineered Mustang with every system designed to make a good driver great and a great driver even better.”

Revs equal power

The transformation begins under the hood, where the reworked 5.0-L DOHC V8 now produces 444 hp (331 kW) and 380 lb·ft (515 N·m), compared to 412 hp (307 kW) and 390 lb·ft (529 N·m) for the regular Mustang GT version of the engine. The team developing the GT’s engine didn’t leave a lot of low-hanging fruit to be exploited for additional power, so the thought of forced induction was considered, reported Mike Harrison, V8 Engines Program Manager. “We decided that would be the wrong thing to do for a Boss 302,” he said, based on the heritage of the engine as a high-revving normally aspirated powerplant.

But to achieve the targeted performance increase, most of the existing hardware would need to be reworked. “It wasn’t one or two parts we had to re-engineer,” he said. “We had to make it breathe, make it rev, and make it durable.”

Addressing the first item, the engine wears an intake plenum containing short intake runners that is taken almost directly from the Daytona Prototype racing program. The heads are cast of a more durable alloy and have thicker walls in the port areas. They are then CNC (computer numerical control) machined to the same port volume as the GT engine but with smoother surfaces for better flow. The computerized porting process takes two and half hours per head, according to Harrison.

This better flow enables more power at higher revs, but those higher revs are challenging when the engine redline climbs from 7000 rpm for the GT to 7500 for the Boss. “What most people don’t realize is that engine stresses increase exponentially as engine speeds rise,” Harrison noted. To reduce that stress, hollow-stemmed valves replace the solid ones for less mass, producing a valvetrain that is “stable to 8400 rpm,” according to Harrison. Exhaust valves are sodium filled for heat resistance.

Forged aluminum Mahle pistons and sinter-forged steel connecting rods bolster the strength of the reciprocating mass, while tri-metal bearing and full-synthetic oil help keep the bottom end spinning freely.

Forged on the track

While most engines are typically developed on the dyno, Ford Racing wanted the more powerful 5.0-L engines as soon as they were available and took them straight to the race track. The on-track data helped the team optimize engine calibration, the design of the oil pan (which provides consistent oil supply during cornering loads of more than 1.0 g), and design of the cooling system. This instrumented testing even let Ford’s engineers in Dearborn recreate Daytona laps in the dyno cells for subsequent testing.

“Working with Ford Racing has been invaluable,” reported Harrison. “They were a wealth of information for setting up torque and power curves for road racing and for identifying areas of concern during track runs that we wouldn’t have considered if we were just building a hot street engine.”

The engine even forced Ford to upgrade its facilities because the company had no dyno that could run at the Boss’s 7500-rpm redline for sustained testing. That testing ultimately equated to contesting the Daytona 250 sports car race 175 times in a row.

Supporting cast

Downstream from the engine is a six-speed manual transmission produced though a Ford joint venture with Getrag, and then the power goes onward to a new driveshaft with a stronger center bearing mount. The driveshaft was the limiting factor in the GT’s 145-mph (233 km/h) top speed, and the new one permits the Boss’s top speed limiter to be set at 155 mph (250 km/h), according to Tom Barnes, Vehicle Engineering Manager.

A piece of simple and cost-effective hardware beneath the Boss 302’s transmission exemplifies the team’s get-it-done approach to improving the car. Welded to a brace attaching to existing transmission mounts is an unimpressive-looking piece of sheetmetal. “It looks like a shovel,” Barnes allows. But that shovel obviates the need for any sort of elaborate transmission cooling by diverting under-car airflow across the existing cooling fins on the bottom side of the transmission.

At the rear, a Torsen limited-slip differential is available as an option for the Boss 302; it is included as part of the $7,999 Laguna Seca track package.

The Boss announces its arrival thanks to a side-pipe-equipped exhaust system that provides a burly rumble. The system is a Faurecia North America-supplied dual exhaust, but it includes diverters ahead of the mufflers that bleed off some sound and release it through undercar side pipes that exhaust directly ahead of the rear wheels.

The car is delivered with a 0.625-in (15.9-mm) restrictor installed in the diverter, but customers could replace the restrictor with an open spacer or turn to the aftermarket for existing devices that let the driver open and close the opening to the diverter from the driver’s seat. The car has a pleasant burble as delivered, which is naturally louder with the restrictor removed, but even then the sound is not objectionable because the side pipes are small and divert only a fraction of the exhaust even without a restrictor.

The Boss’s suspension rides 11 mm (0.43 in) lower at the front and 1 mm (0.04 in) lower at the rear, changes that were dictated by the car’s balance, even though it left the rear a little higher in the air than is fashionable, said Brent Clark, supervisor of the dynamics team. The springs are stiffer than those on the GT, and the rear anti-sway bar is 1 mm thicker.

Adjustable Tokico dampers feature five settings that control both compression and rebound damping, an echo of the adjustable Gabriel shocks on the ’69 Boss 302. The Boss’s shocks adjust with a turn of the screwdriver underhood or in the trunk.

Brakes are four-piston aluminum Brembos up front, squeezing 14-in rotors, while the single-piston rear calipers are carried over from the GT but feature a track-oriented pad supplied by Performance Friction to grip the 11.8-in (300-mm) rear discs.

The 19-in aluminum wheels are 9.0-in (229-mm) wide in the front and 9.5-in (241-mm) in the rear, mounting Pirelli PZero Max tires of 255/40R-19 front and 285/35R-19 rear. Special brake lines that expand 30% less than regular flexible brake lines contribute to improved pedal feel and responsiveness of the brakes.

The steering rack comes from Nexteer Automotive, and it includes electric power steering assist. The driver selects from three settings—normal, comfort, and sport—through the driver information screen on the instrument panel. The changes adjust the amount of assist provided, stiffening or lightening the steering, but without noticeably affecting steering feel.

Interior upgrades

In the cabin, an Auto Meter gauge pack adds supplemental instruments to the top of the dashboard in the manner of add-on gauges on classic American performance cars. Optional Recaro seats come from the Shelby GT500 for extra security during hard cornering, supplemented by an alcantara-wrapped steering wheel.

Despite the Boss’s throwback title and straightforward go-fast mission, it also features some electronic gadgetry that is included to enhance rather than detract from its character. While there is no in-dash GPS navigation or other sophisticated infotainment equipment, the Boss has its advanced electronics in the engine management computer.

Other Ford models offer MyKey, a dedicated key meant for teen drivers that engages an alternate, performance-limiting engine map. For the Boss 302, the feature is renamed TracKey, and it releases an alternate, power-enhancing engine map, reprogramming 300 parameters.

Peak power is unaffected, but the area under the power curve increases as lower-end power is pumped up by revised cam, ignition, and fuel injection timing. While such electronic wizardry could go unnoticed, Ford ensured that TracKey’s operation is apparent by also using it to trigger an idle engine map that includes overlap between the intake and exhaust valves, producing the lumpy uneven idle characteristic of engines with racing cams, such as in the original Boss 302. When combined with the owner-opened side exhaust, it gives the Boss real curb presence.

Laguna Seca

In addition to the limited-slip differential that is optional in regular Boss models, the Laguna Seca package replaces the rear seat with a chassis brace that improves rigidity, which is exploited by still-stiffer springs, 1-mm fatter rear anti-roll bar, and stickier Pirelli Corsa performance competition tires in the same size as the regular Boss’s tires.

Air ducts in the front fascia route cooling air to the front brakes through hoses that connect to vents in the brake backing plates, reducing fade after repeated hard stops on the track. The changes slice 2 s off the Laguna Seca’s lap times compared with the Boss 302's at the former's namesake track, with a 3-ft (0.9-m) reduction in the car’s 60-0 mph (96-0 km/h) braking distance and a 0.1-s improvement in 0-60 mph acceleration time.

Finally, engineers added aerodynamic improvements to secure the car at race speeds. The removable front splitter contributes 35 lb (16 kg) of downforce at 120 mph (193 km/h), and the spoiler produces 45 lb (20 kg) of downforce at the rear of the car. The splitter is directly derived from its counterpart on the racing version of the car, according to the company. “For hard-core Mustang racers who want something they can occasionally drive on the street, to shows, or whatever, Laguna Seca is the car they've been waiting for, and they won’t be disappointed,” Pericak promised.

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